Hi,
First of all, take a deep breath!
You made a mistake, they have admitted that they have made an error in not getting back to you at the correct time, but have confirmed holding you covered. Have a look at
ASKMID
and see if cover is in place on your car. Although this is not definitive, they may have issued a cover note in the office. Give them a chance to sort the issue. After all they want your business and they are not out to upset you for the sake of it.
Reflect on the fact that had they not spotted your error, you might have been paying long term for something that might not have protected you in the event of a claim on the grounds of non or incorrect disclosure.
H